[G-Spot]

Hi Spot - Bambergs work is very good as a general guide but IMO not good for some of the details.

His maths sucks because his stiffness theory only makes sense if you treat every contact between elements as a spring. Which in the case of his machine would be 4 sets of bearings on each of 5 axis meaning his required stiffness from his own calculations would be 20 something meaning he would need a stiffness of 1000N/um and not the 400N/um he claimed.

I think he is right in the way stiffness is like capacitors in series but that means like with capacitors your overall stiffness will be less than your lowest stiffness. The stiffness of the rest of the elements will dictate how much lower, if all the other elements are at least 10 times stiffer then your overall stiffness will be close to the lowest stiffness.

[G-Spot]

Hi Spot - What is the point of burying a steel spaceframe in a concrete casing? One of the structures will be dominate. The steel being 200Gpa will provide a preferred loadpath and the 30GPa concrete just adds mass. Or the concrete having the greater inertia (being outside) will be dominate and the steel will be doing naught. I doubt they will co-operate in a useful way. You have a philosophical issue to resolve here me thinks. Peter

This is like trying to say, If you are pushing a car and a granny comes to help that because you are the dominate force the granny's effort does nothing. If 10 grannys came to help you would it still make no difference?

Anyway it was the vibration analysis that killed the space frame, too hard to dampen all those bells welded together. But I can't believe you are arguing about concrete in steel being a bad idea when most of our modern infrastructure is supported with it. The reason concrete and steel are used together is because of how thermally compatible they are.

[peteeng]

Hi Spot - If your doing manual maths then usually we use the resistor sum analogy for calculating the compliance. So use series or parallel resistor theory or network to calculate the compliance. If your using FEA then use the appropriate contact conditions and it will figure it out for you. I'm sure everyone who has written a thesis has regrets or reservations. I think they should make it obligatory for the author to review a thesis 1 year after written and then write an addendum. That would be interesting. Peter

The reason steel reinforcement is used is to make it stronger at service and ultimate loads and to make it continuous when it cracks ie the steel is doing the work. Modern steel or synthetic fibre construction does not use continuous steel reo anymore. Service strength or ultimate strength is not an issue with machine elements but if it cracks then you have no tensile stiffness. Portland will macro and micro crack, unfortunately cracking is a given, use engineering grout. I think the granny analogue is not valid in this case. Pushing objects and preferential load paths are a bit different. But you keep at it. The grail is out there...

Before concrete infrastructure we used steel frames and facades and before that we used solid masonry and masonry has been up for 5000 years +, steel frames for a couple of hundred years if looked after... We are now paying the price for cheap concrete construction as buildings have to be torn down, dams reconstructed etc as the steel gets rusty and jeopardises the structure. Not that rusty reo will be a problem in your machine as it unlikely to be used in 40 - 50 years time... The reason concrete is used is because its cheap....simples. Within itself its a fine material used correctly, in combo with steel you have to be careful for machine applications.

[G-Spot]

Hi spot a large scale printer - Peter

UMaine’s novel polymer 3D printer surpasses former Guinness World Record | CompositesWorld

They took 2 I-beam gantry beams and fixed them together, because when you are going to build that sustainable green eco thing whatever setting up a 50 ton gantry crane is the sustainable thing to do.

The future for construction is those flying drones that they are using to 3D print structures. Operating in swarms.Making parts using a piece of steel as a reference when the metric meter is derived from light, is history.

[G-Spot]

Hi Spot - If your doing manual maths then usually we use the resistor sum analogy for calculating the compliance. So use series or parallel resistor theory or network to calculate the compliance. If your using FEA then use the appropriate contact conditions and it will figure it out for you. I'm sure everyone who has written a thesis has regrets or reservations. I think they should make it obligatory for the author to review a thesis 1 year after written and then write an addendum. That would be interesting. Peter

The reason steel reinforcement is used is to make it stronger at service and ultimate loads and to make it continuous when it cracks ie the steel is doing the work. Modern steel or synthetic fibre construction does not use continuous steel reo anymore. Service strength or ultimate strength is not an issue with machine elements but if it cracks then you have no tensile stiffness. Portland will macro and micro crack, unfortunately cracking is a given, use engineering grout. I think the granny analogue is not valid in this case. Pushing objects and preferential load paths are a bit different. But you keep at it. The grail is out there...

Before concrete infrastructure we used steel frames and facades and before that we used solid masonry and masonry has been up for 5000 years +, steel frames for a couple of hundred years if looked after... We are now paying the price for cheap concrete construction as buildings have to be torn down, dams reconstructed etc as the steel gets rusty and jeopardises the structure. Not that rusty reo will be a problem in your machine as it unlikely to be used in 40 - 50 years time... The reason concrete is used is because its cheap....simples. Within itself its a fine material used correctly, in combo with steel you have to be careful for machine applications.

Concrete has 10 times less stiffness than steel but it is 100 times cheaper, if you have x amount of money and you want the most stiffness then you choose concrete.

Fibers need to be in contact with other fibers to have tensile strength, like in a rope. Ever spliced a rope? doesnt work if you just loop it over, you have to tightly weave the fibers against each other .Do you not remember when every boat building company in the USA started to make boats by applying resin mixed up with loose fibers and now you cannot get boat insurance in the USA if your boat was made this way. Exact same arguments about why it works but the reality was it makes the resin weaker and just stops it falling into pieces when it does break. See the cement test video, if you didnt see the actual results it would seem the cement with fibers was better at resisting force. It just makes cement look cosmetically better, less surface cracking with aging but structurally it is weaker. And the concrete core that had steel fibers in it, you could see that the thing cracked open in the fault lines that the steel was in. This is why you filter any grass or any other fiberous material from the sand you use when making cement...because it weakens cement, if they were so great then why for the last 1000 years have builders been filtering out the grass and vegetation from the sand they use.

[peteeng]

"fibres need to be in contact with other fibres to have tensile strength" absolutely wrong. I have spliced many ropes and that is a totally different game to fibre composites. Aircraft wings and fuselages are made of fibres held together with the fibres not touching so you had better not fly somewhere. Vegetation rots and leaves voids that's why you separate it. Fibers designed for concrete do not rot or corrode. Your mental arguments need reality checks. Keep at it, you will figure it out eventually. Your Grail is moving away from you faster than you are gaining, you had better start pedalling faster... Peter

[G-Spot]

OK just finished up analysis of steel v concrete for this application.

Here's a beam of house concrete 500x500 across a 1m gap with a load applied to a 300x300 section in the middle.

Then the same simulation using a 300mm x 300mm x 10mm steel beam across the same 1m gap.

The concrete beam cost $50 using regular concrete without any reinforcement.

The steel beam cost $125.

The concrete failed at 50 metric tons and its deflections were consistently less.

The steel failed at 20 metric tons and its deflections were poor from the start.

Steel maybe a stiffer material than concrete, but for this application it is a lot less stiffer than the concrete employed for less than half the price.

[G-Spot]

"] Aircraft wings and fuselages are made of fibres held together with the fibres not touching so you had better not fly somewhere.

Incorrect the fibre used in aircraft and boats is woven mat that already has incredible tensile strength from end to end before any resin is added, the same way that the reinforcing in concrete has incredible tensile strength from end to end before the cement is added, how the joins are woven with each other is the same as how a rope is spliced together. There is a book of regulations on how the ends of steel most be woven together when making steel reinforcing.

They do not make aircraft or boats(anymore) by chopping up small strands of fiber or steel and then adding them to the mix. And when they do have to join fiber mats or rebar mid structure there is a minimum overlap required between the two pieces and they must be held tight together before the resin or concrete is added,

[G-Spot]

Meanwhile back with the thermal analysis of the sections of concrete and the plates attached to them continues.

After seeing the stress maps from the concrete v steel analysis I can see that the concrete is never going to be under any tensile forces. Only when you have over 10 tons sitting in the middle do tensile forces appear on the bottom of the concrete, so that is going to save me a lot of time.

The attached files show that I only have to worry about the corners of the steel plate on the concrete, so I will make sure they chamfer the bottom edges and round the corners on my plates.

I can also see the correct strategy for minimizing distortion of the steel plates through choosing the right thickness of materials and shape. Placement is also important. Going to spend the next week coming up with a mechanical solution that minimises distortion of the steel plates due to thermal differences between the cement and steel.

I wont be doing any detailed machine drawings until I have my screws and bearings in hand, I see a large majority of these type of builds end up having to machine extra inelegant and unstiff fixes due to a change in how the screw supports or motor mounts had to be fitted. I want my plates to come ready to fix the rails, screws and motors without any further mods. The best way of doing that, would be to assemble the parts on a flat surface and check all measurements. Also you see stuff like where the cable comes out the motor will need to clear a few millimeters or you will never be able to adjust, remove something etc etc.

[peteeng]

Hi Spot - aircraft and high performance boats do NOT use woven mat. They use straight fibres at a fibre volume ratio of around 55-60% so they have space around them for the resin. Really modern stuff uses nano fibres in the resin mix. Keep at it....Your not comparing apples to apples with a 500x500mm concrete beam vs a 300x300mm steel beam. Geometry will always win in that case. In machine design the maximum size component is defined by the size of the machine & the space available for that part. So you need to compare the same external size beams. What costs do you use for concrete and steel? Peter

[G-Spot]

]Your not comparing apples to apples with a 500x500mm concrete beam vs a 300x300mm steel beam. Geometry will always win in that case. In machine design the maximum size component is defined by the size of the machine & the space available for that part. So you need to compare the same external size beams. What costs do you use for concrete and steel? Peter

I am comparing apples with apples, any machine made using the usual 250mm x 250mm x 10mm steel column ends up with at least a 1m x 1.5m base after they weld all the stiffners and supports on.

I am going to use 500mm x 500mm concrete and the base will only be 500mm x 1000mm. It will occupy less space and be 10 times stiffer and twice the strength of the same size machine.

Such is the power and stiffness of concrete compared to steel.

Who said there is a quality to quantity?

[G-Spot]

What costs do you use for concrete and steel? Peter

The real DIY costs, I can get concrete delivered in a truck for the trade price, but the price I used is what it costs me to hire a mixer and vibrator and the cost of the bags and sand and stone.
The same with the steel, real delivered to your door prices, not the current stock exchange price.

[peteeng]

Again Spot - What are the $/kg steel and $/kg concrete you used? I don't want to argue with your costs I want to know the cost ratio to check your comparisons. Peter

[G-Spot]

aircraft and high performance boats do NOT use woven mat.

https://www.youtube.com/shorts/JheQe24xtB4

They use multiple single strands on a roller as seen in this video, literally a giant sewing machine knitting a mat directly onto the part, aint nobody using small strands thrown into a mix like you propose.
And it is effectively weaving the mat directly onto the mold, the same patterns and the direction of the threads giving tensile strength in the direction they want it.
The end result is the same as with the woven mats, but laying the carbon fibre down directly onto the mold gives them the ability to keep the same tension and direction the entire run of the thread no matter the complexity of the surface. When you lay a linear mat down on a contoured surface the fibers do not have same tension when it is finished.

The point is the reinforcing wire, thread, rebar has tensile strength across the part WITHOUT the resin or concrete. You are saying that throwing broken threads into the resin or concrete at random gives it the same tensile strength when they never had any tensile strength to begin with before the resin or concrete even set.

AND as can be seen from my concrete v steel simulations, the concrete for machine use is never going to be in tension, so why are you proposing to add chopped fibers to supposedly increase its tensile strength at the expense of its compressive strength which it is going to need.

This super concrete with fibers for machine use is so busted, proven to make the machine weaker and likely crack.

[peteeng]

Sorry Spot - Weaving, knitting and tape laying are totally different processes. It is NOT a sewing machine and it is not knitting or weaving. You'll get there one day. Plus if you load a structure there is always tensile strain somewhere. Even if you compress something there is tension somewhere. Look up Hertian stresses... Peter

[G-Spot]

Again Spot - What are the $/kg steel and $/kg concrete you used? I don't want to argue with your costs I want to know the cost ratio to check your comparisons. Peter

Do the math.

500 x 500 x 1000mm = 0.25 cubic meters = 2.5 bags of cement which is $(US)15 here plus 5 bags of sand and 5 stone $20

300 x 300 x 10 x 1000mm is 91.2kg of steel which is $(US) 104.88

Still less than half the price of steel after you paid for the mixer and vibrator and at least double the stiffness and strength of the steel.

And of course a 300mm x 300mm hollow steel pipe is going to ring like a church bell. So you going to want to fill it with something.

[G-Spot]

Sorry Spot - Weaving, knitting and tape laying are totally different processes. It is NOT a sewing machine and it is not knitting or weaving. You'll get there one day. Plus if you load a structure there is always tensile strain somewhere. Even if you compress something there is tension somewhere. Look up Hertian stresses... Peter

Whom am I going to believe you, or my lying eyes....lol......anyone watching that video sees a machine laying down threads in patterns like the spindle does on a sewing machine. I would be keen to see your rebuff my theories using your wizard FEA skills and not just appeals to authority. You must have tested your theories on concrete and taken photos of the micro cracks etc, what thickness were you casting with?

[G-Spot]

Not weaving a mat at all, any resemblance to weaving a mat is purely coincidental.
What we have here is a machine throwing down pieces of fiber into a random mix.
It's not weaving anything using single continuous fiber across the part in the directions it wants the tensile strength to be.
You know like how mats are made.

https://www.youtube.com/shorts/tht1JI0LJ5c

[peteeng]

Hi Spot - Again sorry - the fibre composite industry has very specific definitions of weaving, knitting and tape laying,. I have been involved in all of these. The machine in the video is a tape layer. The tape is prepreg epoxy and carbon fibre. The resin is formulated for a specific "tack' so it is heated via an infra red element that you can see the glow from. It comes off the roll and is just like sticky tape. There is no stitching thread (sewing) or intertwining of fibres (knitting).

I suggest you read up on mechanics of solids... There is enough weight of evidence that Portland cement cracks and that every civil design code is based on the concrete cracking so the code has to mitigate the cracking issue with "reinforcement" which is a poor descriptor for what it does. FEA is only as good as your assumptions used and the interpretation within those assumptions. A manual calc is as good for something simple...

I have tested many materials personally or at labs. Concrete or grout - I have various samples that I have used for stepping stones around the place... some are quite expensive! steps...

Your saying that 0.25m3 is $35 USD and that 91.2kg od steel is $105 USD. So take your concrete at 2400kg/m3 is 600kg so concrete is 0.058 $/kg and steel is $1.15 per kg.

around here concrete cost around $250/m3 laid so thats 0.25 $/kg. At the hardware 20kg of cement costs $8 AUD so that makes 26kg of concrete so thats 0.31 $/m3

I'll use $0.10 USD / kg and steel at $1.00 USD/kg so the maths is easy.... Peter

[G-Spot]

Here's a primitive poverty stricken outfit that didn't take the red pill on how to use fibers.
Still weaving away with his primitive mats.
They are going to be out of business soon if they don't embrace chaos theory when it comes to fibers in a matrix.

https://www.youtube.com/watch?v=4GddDvAD3pY